a:hover和a.active的意义和作用是什么

header > .container > nav > a.home{background: #433b90;}

header > .container > nav > a.course{background: #017fcb;}

header > .container > nav > a.actual{background: #78b917;}

header > .container > nav > a.plan{background: #feb800;}

header > .container > nav > a.faq{background: #f27c01;}

header > .container > nav > a.notes{background: #d40112;}

header > .container > nav > a:hover,

header > .container > nav > a.active{padding-bottom:7px; }